Ulcerative colitis (UC) is one of the chronic intestinal disorders known as inflammatory bowel disease (IBD). It affects hundreds of thousands of Americans with about 25-30% being children. UC causes considerable suffering with abdominal pain, diarrhea, bleeding, and weight loss and for unknown reasons is often more severe in children than adults. Longstanding disease carries a high risk of colon cancer. Ideally, UC is adequately controlled with mesalamine, a 5-aminosalicylate with a favorable benefit: risk profile. Unfortunately, mesalamine alone is often not sufficient requiring step-up therapy with corticosteroids (steroids), potent immunosuppressive medications (IM) with major risks, or surgery to remove the colon. There are a lack of controlled data on the treatment of UC in children and virtually no studies that provide guidance to clinicians as to which children are going to do well with mesalamine alone and who is going to do poorly and need increasing medication exposure or surgery. We hypothesize that a combination of clinical, genetic, and immunologic tests performed at diagnosis may allow construction of a model for individualized treatment and thereby improvement of current outcomes. Specifically, we will conduct a clinical trial of standardized medical therapy for 430 children newly diagnosed with UC at 24 pediatric IBD centers in North America (Predicting Response to Standardized Pediatric Colitis Therapy: The PROTECT Study). Using a clinical protocol that is designed to provide optimal care and be responsive to disease severity, as well as state of the art technology to monitor medication adherence, we will subsequently determine the primary clinical outcome of clinical remission at one year on mesalamine only without the concurrent use of steroid medications or the need for more potent immunosuppressive medications or surgery. Biospecimens including blood, stool, and colonic tissue will be obtained at diagnosis and during follow-up, and pre-specified clinical, genetic, environmental, and immune factors will be determined and tested for their impact upon the primary clinical outcome as well as mucosal healing at one year. When possible patients will be followed beyond one year and up to 2-5 years depending upon time of entry into the study. The collective results of the PROTECT study will have a significant and sustained impact upon the field by: 1) providing data regarding response to standardized therapy maximizing the likelihood of response to mesalamine, 2) identifying novel biologic pathways associated with treatment response, and 3) establishing a repository of clinical, genetic, and immune data, as well as biospecimens, that can be used by for future ancillary studies. Ultimately, results of PROTECT will be integrated with those of an ongoing prospective study of 1100 pediatric Crohn's Disease (CD) patients sponsored by the Crohn's and Colitis Foundation of America (CCFA), the RISK study, to provide a powerful new platform for discovering mechanisms which drive pathogenesis and clinical outcomes in pediatric IBD.